The voltage conversion device is able to convert an inputted alternating voltage to a direct voltage and output the same to electrical appliances. In a typical usage scenario, the voltage conversion device can be, for example, an electronic ballast which can convert a power network voltage in a form of an alternating voltage into a direct voltage and output to a light emitting diode (LED) or other electrical appliances.
The voltage conversion device can have a plurality of voltage connectors, and the alternating voltage is fed to the voltage conversion device via different voltage connectors. Since the direct voltage outputted by the voltage conversion device varies, one voltage conversion device can be applied to electrical appliances with different powers.
Patent Literature 1 (CN101982017A) discloses a voltage conversion device, and FIG. 1 is a schematic diagram of the voltage conversion device of the Patent Literature 1. As shown in FIG. 1, the voltage conversion device 1 has voltage connectors 2 and 3, and the alternating voltage fed from the voltage connector 2 or 3 sequentially goes through and is processed by an electromagnetic filter 4, a bridge rectifier 5, a direct voltage intermediate circuit 6, a half bridge inverter 7 and a resonant circuit 8 to become a direct voltage, and is outputted from output terminals 9 and 10 into an electrical equipment 11.
In FIG. 1, the voltage conversion device 1 further has a transformer T, a resistor R and a control unit 12. When the alternating voltage is fed from the voltage connector 3, a current flows through a primary winding W of the transformer T to generate an induced current in a secondary winding W′ and generate a voltage difference across the resistor R. When the control unit 12 detects a voltage difference across the resistor R, it can be determined that the alternating voltage is fed from the voltage connector 3, and a control signal corresponding to the voltage connector 3 is outputted to the half bridge inverter 7 to control the two switches in the half bridge inverter 7 to be alternately turned on, so that the voltage conversion device 1 outputs a corresponding direct voltage. On the contrary, when the control unit 12 detects that no voltage difference is generated across the resistor R, it can be determined that the alternating voltage is fed from the voltage connector 2, and a control signal corresponding to the voltage connector 2 is outputted to the half bridge inverter 7 to control the two switches in the half bridge inverter 7 to be alternately turned on, so that the voltage conversion device 1 outputs a corresponding direct voltage.
In prior art, other methods may be employed to cause the voltage conversion device to output different direct voltages and currents, for example, switching control on the secondary side of the voltage conversion device, or switching control on the primary side of the voltage conversion device, etc.
It should be noted that the above introduction to technical background is merely for the purpose of a clear and complete description of the technical solutions of the present application and for a better understanding by those of ordinary skill in the art. The above technical solutions should not be considered to be well-known to those of ordinary technicians simply because these solutions are to set forth in the section of background art of the present application.